Date: Wed Oct 8 09:40:57 2008

Author: David Kardelis

Subject: Re: in need of some good multimeters

Post:

Using the oscope you can get phase relations, I figured once the circuits were in use nice to show them that peak voltage and RMS voltage are not the same but there is a relationship. We tell them all the time, but pretty easy to show with data.

Also in testing their speaker parameters they use a DMM to get the impedance of their speakers. The cheap meters were useless as the results were almost random at higher frequencies.

dave

-----Original Message-----
From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of Bernard Cleyet
Sent: Tuesday, October 07, 2008 4:38 PM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] in need of some good multimeters

Finally I'm informed one reason for a very expensive DMM. However,
if one is using an o'scope, why the meter?

One of the two intermediate lab's (Santa Cruz) experiments is (was?)
low frequency impedances. Included are various* combos of caps,
inductors and resistors. The concerned equipment is an audio
oscillator and an X-Y Tektronix 'scope (ca 1980). Its response (0
=> 100 kHz) is very good w/ identical amps. That's it. The circuit
elements are in boxes and not opened until the students have
determined the circuit.


* also a thermistor, lamp and diode. A transformer for impedance
matching is supplied w/ the thermistor and lamp. Also a Keithley is
available for the > 100 megohm resistor. The students are not
informed just the cabinet is not locked. One of the resistors is a
heavy wire. When they can't measure it, they are permitted to open
the box and continue. They discover why a ten + A regulated supply
is available. The are not permitted to stop until they have
discovered four point technique.

bc instructed the TAs not to "give the game away", just give hints
Socratically.

p.s. Fluke 187 spec.

http://labcontrol.cicese.mx/pdf/Fluke.pdf



On 2008, Oct 07, , at 14:39, David Kardelis wrote:

> I ended up getting Fluke 187's. The fuses are easy to get to, only
> need a dime/flat blade screw driver. Takes about 2 minutes total
> including finding a screwdriver.
>
> If the wire are hooked up wrong the meter beeps at you and displays
> Leads/Fuse. I have been using them for 5 years, haven't had to
> replace more than dozen fuses. The last one due to an instructor
> blowing the fuse.
>
> I needed/wanted the Fluke because I was having the students do ac
> measurements on speaker/cross-over networks. The cheap meters would
> not give an accurate voltage measurement at higher frequency. I
> used to have them plot meter voltage/O-scope voltage vs freq. With
> the fluke you get a straight line with slope of 1/ sqrt(2), on the
> cheap meters it was a parabola of sorts. Not linear at all.
>
> dave
>
>
cut


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